OCR Text |
Show 264 MR. E. B. POULON ON THE PROTECTIVE [Mar. 1, in the former has been previously alluded to. A friend has raised the objection that the moth imitates a piece of twig cut cleanly at both ends, an object which cannot be found in nature unassisted by art. The reply of course is that the purple aud grey colour of the sides of the suggested cylinder, together with its pale ochreous ends -the one appearing to be cut transversely, the other obliquely across- present a most perfect resemblance to wood, with that particular condition of texture induced by decay, in which alone the tissue will break shortly and sharply as if cut, on the application of slight pressure or the force of an insignificant blow. Ln coitu the sticklike appearance is admirably preserved, the two insects looking like a single twig (Newman). It was clear from the energetic and instantaneous attacks made on these moths, that tbe Lizards expected them to be palatable and that the unpleasant quality is incidental and useless. It was very interesting to observe that the continuity of the unpleasant properties through the different stages in this species is accompanied by a gradual lessening in their powers. The larva was certainly disliked far more than the other stages, and the pupa seemed to be more neglected than the imago, the latter being eaten in large numbers, although often after preliminary tasting and temporary rejection. This fact also favours the explanation given above of the origin and meaning of the unpleasant qualities in the two terminal stages. In the case of O. antiqua, we have a most inconspicuous insect with the same unpleasant taste. Here also the same explanation probably holds good as far as the origin of the qualities is concerned, for we have previously seen that its most brightly-coloured and freely exposed larva was disregarded by all the birds. In this case I do not yet feel certain that the property may not be of some value to the female imagos ; for it would be impossible to find a more helpless insect, without even the power of attempting to escape by walking. More observations are greatly needed, and it would be especially interesting to ascertain whether the quickly-flying males are equally disliked as food. The pupa of P. bueephala has been already alluded to. Confirmation is, I think, needed of Newman's statement that fowls eat this pupa freely, for the dislike of the Lizards was extremely marked, and as a rule these animals are less delicate than birds. The pupae of V. io and V. urtica possess the highest form of protective resemblance; and here, again, Jenner Weir's observation, I think, should be repeated, as the Lizards acted so very differently with the latter species. Is it quite certain that the birds were aware of the presence of these generally motionless pupa? in Jenner Weir's experiments? The consideration of the fourth subdivision of the list, including species of Arthropoda other than the Lepidoptera, enforces very strongly the conclusions of the rest of this paper,-that defensive habits and structures may exist in almost any kind of combination, so that we find plenty of instances of the co-existence of unpleasant attributes with protective resemblance, as well as with a " warning " appearance. |